Create a file c:\I_have_to_do_this.txt, and, before starting simplex.exe, write into this file, in plain English, what Simplex is supposed to do.

In the unlikely case that simplex.exe has a different way of getting its user input, it would help to describe how you usually tell simplex.exe what it has to be done (i.e. without using Perl) - say, passing arguments on the command line, setting up a socket connection, setting environment variables, or whatever. Than we can help you better....